Magnetrons

ABSTRACT

An electrically tunable axial cathode magnetron comprises adjacent to the cathode and sufficiently close to the cathode to be in the space charge formed when the magnetron is in use, an additional electrode arrangement. The additional electrode arrangement is non-emitting and coaxial with the cathode and symmetrical with the magnetron anode axis.

United States Patent Pickermg 1 Apr. 25, 1972 [54] MAGNETRONS 2,930,933 3/1960 Griffin, Jr. et a1. sis/39.63 2,748,277 5/1956 Haagensen 315/3963 X lnvemori Alan g Pickering, Chelmsfofd, 3,158,780 11/1964 Gerlach BIS/39.63 X gland 3,020,445 2/1962 Weinstein... ...3l5/39.73 X 3,274,433 9/1966 Peterson..... ...3l5/39.63 X [73] Assignee. English Electric Valve Company Limited, 3,418,522 12/1968 Cook I I 315/3963 England 2,782,342 2/1957 Kilgore sis/39.53 x [22] Filed: O t, 5, 1970 2,953,714 9/1960 Rostas ..315/39.63 PP 78,108 Primary Examiner-Herman Karl Saalbach Assistant Examiner-Saxfield Chatmon, Jr. 30 Foreign Application Priority Data Dec. 2, 1969 Great Britain ..58,694/69 ABSTRACT An electrically tunable axial cathode magnetron comprises UoS- adjacent to the athode and sufficiently lose to the athode [51] Int.Cl. ..H01j 25/50 to be i th a e harge formed when the magnetron is in [S8] Fleld of Search ..3l5/39.63, 39.53, 39.73, 39.57, use, an additional electrode arrangement. The additional elec- 3l5/39.55 trode arrangement is non-emitting and coaxial with the cathode and symmetrical with the magnetron anode axis.

56 R f I 1 e erences cued 9 Claims, 1 Drawing Figure UNITED STATES PATENTS 3,084,280 4/1963 McLaughlin ..3l5/39.63X

Patented April 25, 1972 ATTOPNEYZ MAGNETRONS This invention relates to magnetrons and has for its object to provide improved electrically tunable magnetrons, that is to say to magnetrons the frequency of which can be varied purely electrically and without mechanical movement of any part.

The invention is applicable to any magnetron of the kind having an electron-emitting cathode on the axis of an anode system which may be of any type known per se, e.g. a multicavity anode system of the so-called hole and slot type or a so-called rising sun anode system, or any other form of coaxial anode system, whether strapped or not. For convenience and brevity of reference magnetrons of this kind will hereinafter be referred to as axial cathode magnetrons.

According to this invention an electrically tunable axial cathode magnetron comprises adjacent the cathode thereof and close enough thereto to be in the space charge which is formed in the neighborhood thereof when the magnetron is in use, an additional electrode arrangement which is substantially non-emitting, substantially coaxial with the cathode and substantially symmetrical with respect to the axis.

In the preferred embodiments of the invention the additional electrode arrangement is constituted by a single electrode which is spaced end on to the cathode and is coaxial therewith.

The additional electrode arrangement may be electrically connected to the cathode was to be at the same potential. If this is done electrical tuning of the magnetron is effected by varying the anode current thereof, the most practical and convenient way of doing this being by varying the DC voltage on the anode system with respect to that on the cathode and on the additional electrode arrangement. It is, of course, well known electrically to tune a magnetron by varying the anodecathode DC voltage but when this is done with a magnetron in accordance with this invention the fact that the additional electrode arrangement is close enough to the cathode to affect the space charge thereof, results in the obtaining of a very considerably increased change of frequency of oscillation for a given variation of anode potential than is the case with an otherwise similar comparable known magnetron.

Preferably, however, means are provided for applying to the additional electrode arrangement a variable negative DC potential with respect to the cathode. By varying this potential a substantial and practical range ,of tuning is obtainable without varying the applied anode potential.

The additional electrode arrangement should be made of a material having as low thermionic and secondary emitting properties as possible. Examples of suitable materials for said additional electrode arrangement arecarbon, graphite, carburized tungsten, molybdenum and titanium.

In a preferred embodiment of the invention two structures in line with one another are provided on the axis of the magnetron anode system. These structures are spaced a short distance apart end to end. One of them is a hollow cylindrical thermionic cathode housing a cathode heater and the other is a hollow additional cylindrical electrode of at least approximately the same diameter as the thermionic cathode. The two structures may be of equal lengths but this is not essential. Preferably a pair of discs constituting a pair of so-called endhats are provided, one at that end of the thermionic cathode cylinder remote from the additional electrode and the other at the end of the additional electrode remote from the thermionic cathode.

The invention is illustrated in the accompanying drawing which shows in schematic cross section a preferred embodiment. In the drawing the anode and output systems are indicated purely schematically since the invention is not concerned therewith. As already stated the anode system may be of any known type adapted to operate with a coaxial cathode within it, e.g. an anode system of the resonant cavity hole and slot type or of the rising sun type.

Referring to the drawing the magnetron illustrated therein has a known anode system 1 which is represented by the crosshachured part of the drawing and a known output system 2 of the waveguide type as indicated purely schematically.

The axis of the magnetron is indicated by the chain line X- X. The applied magnetic field (applied by means not shown) is in the direction of the arrows M. A thermionic cathode 3 and an additional electrode 4 having a common axis in the line X-X are spaced apart end to end and together (including the space between them) extend over rather more than the axial dimension of the anodes. The cathode 3 contains a heating filament 31 and at the end thereof remote from the electrode 4 is a disc constituting an end hat 32. This cathode is supported by a support 33 which incorporates the necessary external connections for the cathode 3 and its heater 3]. The cathode 3 is a hollow cylinder.

The electrode 4 is also a hollow cylinder but it is (as far as is conveniently possible) not electron emitting. It is made of a material of very low thermionic and secondary emission, e.g. carbon, graphite, carburized tungsten, molybdenum or titanium. The electrode 4 is carried by a support 41 by means of which external connection can be made thereto. An end hat 42 similar to the end hat 32 is provided as shown. The two electrodes 3 and 4 are shown as of about the same length but this is not necessary.

The magnetron illustrated can be variably tuned in either of two ways. In one way the two electrodes 3 and 4 are electrically connected together and tuning is effected by varying the DC potential applied between these electrodes on the one hand and the anode system on the other. Tuning by varying the anode current usually by varying the anode-cathode DC potential is of course well known per se. However the variation in frequency of oscillation obtainable from a magnetron as illustrated, for a given variation of anode current, is substantially greater than that obtainable in a comparable known magnetron for the same anode current change.

Preferably, however, the two electrodes 3 and 4 are not connected together and tuning is effected by applying a variable negative DC potential to the electrode 4 with respect to that applied to the electrode 3. With tuning in this manner variation of oscillation frequency over a relatively wide range can be obtained by means of an applied DC potential which is varied, for tuning purposes, over a relatively small range, and without incurring the inconveniences and disadvantages of varying the anode-cathode potential.

Iclaim:

1. An electrically tunable magnetron having a magnetic field applied axially thereof, comprising in combination:

an anode having a bore therethrough extending axially in the direction of the applied magnetic field;

a cathode having at least a portion thereof disposed within said bore and defining an annular space therewith; means for causing said cathode to emit electrons to form a space charge within said bore;

an additional electrode arrangement having at least a portion thereof disposed within said bore in a region thereof axially spaced from that region within which said cathode is situated, said additional electrode arrangement being made of substantially non-emitting material and being located sufficiently close to said cathode as to be in said space charge; and

means for electrically tuning the magnetron.

2. A magnetron as claimed in claim 1 wherein the additional electrode arrangement is constituted by a single electrode which is spaced end on to the cathode and is coaxial therewith.

3. A magnetron as claimed in claim 2 wherein said means for electrically tuning the magnetron comprises means electrically connecting said additional electrode arrangement to the cathode so as to be at the same potential.

4. A magnetron as claimed in claim 3 wherein said means for electrically tuning the magnetron also includes means for varying the anode current thereof by varying the DC voltage on the anode system with respect to that on the cathode and on the additional electrode arrangement.

5. A magnetron as claimed in claim 2 wherein said means for electrically tuning the magnetron also includes means for applying to the additional electrode arrangement a variable negative DC potential with respect to the cathode.

low cylinder; said cylinders being at least approximately of the same diameter and disposed in alignment with each other on the axis of said magnetron.

9. A magnetron as claimed in claim 8 wherein a pair of discs constituting a pair of so-called end-hats are provided, one at that end of the thermionic cathode cylinder remote from the additional electrode and the other at the end of the additional electrode remote from the thermionic cathode. 

1. An electrically tunable magnetron having a magnetic field applied axially thereof, comprising in combination: an anode having a bore Therethrough extending axially in the direction of the applied magnetic field; a cathode having at least a portion thereof disposed within said bore and defining an annular space therewith; means for causing said cathode to emit electrons to form a space charge within said bore; an additional electrode arrangement having at least a portion thereof disposed within said bore in a region thereof axially spaced from that region within which said cathode is situated, said additional electrode arrangement being made of substantially non-emitting material and being located sufficiently close to said cathode as to be in said space charge; and means for electrically tuning the magnetron.
 2. A magnetron as claimed in claim 1 wherein the additional electrode arrangement is constituted by a single electrode which is spaced end on to the cathode and is coaxial therewith.
 3. A magnetron as claimed in claim 2 wherein said means for electrically tuning the magnetron comprises means electrically connecting said additional electrode arrangement to the cathode so as to be at the same potential.
 4. A magnetron as claimed in claim 3 wherein said means for electrically tuning the magnetron also includes means for varying the anode current thereof by varying the DC voltage on the anode system with respect to that on the cathode and on the additional electrode arrangement.
 5. A magnetron as claimed in claim 2 wherein said means for electrically tuning the magnetron also includes means for applying to the additional electrode arrangement a variable negative DC potential with respect to the cathode.
 6. A magnetron as claimed in claim 1 wherein the additional electrode arrangement is of low thermionic and secondary emitting properties.
 7. A magnetron as claimed in claim 6 wherein the additional electrode arrangement is made of carbon, graphite, carburized tungsten, molybdenum or titanium.
 8. The magnetron as defined in claim 1 wherein said cathode comprises a thermionic portion in the form of a hollow cylinder and a cathode heater within said cylinder, and said additional electrode arrangement comprises a second hollow cylinder; said cylinders being at least approximately of the same diameter and disposed in alignment with each other on the axis of said magnetron.
 9. A magnetron as claimed in claim 8 wherein a pair of discs constituting a pair of so-called ''''end-hats'''' are provided, one at that end of the thermionic cathode cylinder remote from the additional electrode and the other at the end of the additional electrode remote from the thermionic cathode. 